The fracture network of hydraulic crack is significantly influenced by the bedding plane in coalbed methane extraction.Under mode Ⅱ loading,crack deflection holds a key position in hydraulic cracking,especially in hy...The fracture network of hydraulic crack is significantly influenced by the bedding plane in coalbed methane extraction.Under mode Ⅱ loading,crack deflection holds a key position in hydraulic cracking,especially in hydraulic shearing.This study first analyzed the crack deflection theory of layered rock.The semi-circle bending test under asymmetric loading is performed,and the four-dimensional Lattice Spring Model(4D-LSM)is established to examine how the bedding parameters affect coal crack propagation under mode Ⅱ dominant loads.The 4D-LSM results are comparable to the coal loading test results under quasi-mode Ⅱ and the analytical prediction of crack deflection theory.During mode Ⅱ loading,the coal crack propagation is greatly influenced by the angle,strength,and elastic modulus of the bedding plane,while the effects of thickness and spacing of bedding are insignificant.The crack of coal tends to propagate towards the bedding,following a decrease in bedding angle,a decrease in bedding strength,and an increase in elastic modulus.With higher bedding strength,spacing,and thickness,the peak load on the coal sample is higher.The influences of bedding strength,elastic modulus,spacing,and thickness on the peak load of coal samples and its anisotropy gradually decrease.It is proved that compared with the tangential stress ratio and traditional energy release ratio theories,the corrected energy release ratio criterion can more accurately predict the direction of crack deflection of coal,especially under mode Ⅱ loading.The results can provide assistance in the design of initiation pressure and fracturing direction in coal seam hydraulic fracturing.展开更多
基金financially supported by the National Natural Science Foundation of China(Grant Nos.52225402,U1910206)the National Key Research and Development Project of China(Grant No.2022YFC3004602).
文摘The fracture network of hydraulic crack is significantly influenced by the bedding plane in coalbed methane extraction.Under mode Ⅱ loading,crack deflection holds a key position in hydraulic cracking,especially in hydraulic shearing.This study first analyzed the crack deflection theory of layered rock.The semi-circle bending test under asymmetric loading is performed,and the four-dimensional Lattice Spring Model(4D-LSM)is established to examine how the bedding parameters affect coal crack propagation under mode Ⅱ dominant loads.The 4D-LSM results are comparable to the coal loading test results under quasi-mode Ⅱ and the analytical prediction of crack deflection theory.During mode Ⅱ loading,the coal crack propagation is greatly influenced by the angle,strength,and elastic modulus of the bedding plane,while the effects of thickness and spacing of bedding are insignificant.The crack of coal tends to propagate towards the bedding,following a decrease in bedding angle,a decrease in bedding strength,and an increase in elastic modulus.With higher bedding strength,spacing,and thickness,the peak load on the coal sample is higher.The influences of bedding strength,elastic modulus,spacing,and thickness on the peak load of coal samples and its anisotropy gradually decrease.It is proved that compared with the tangential stress ratio and traditional energy release ratio theories,the corrected energy release ratio criterion can more accurately predict the direction of crack deflection of coal,especially under mode Ⅱ loading.The results can provide assistance in the design of initiation pressure and fracturing direction in coal seam hydraulic fracturing.
